A unique ranking of the third-party logistics companies in North America includes listings of the largest freight brokerage firms, freight forwarders, warehouse operators and dedicated contract carriage service providers.

The five-member NTSB is an independent agency charged with investigating transportation accidents.

Hersman was appointed to the five-member NTSB in 2004 by President George W. Bush and was then reappointed by President Obama to a term set to expire this year.

An NTSB spokeswoman declined to comment on Sunday, as did the White House, the Journal reported.

Los Angeles Mayor Antonio Villaraigosa (D), who has also been mentioned as a DOT candidate, said in a statement Friday that he was committed to finishing his term, which ends June 30, the Associated Press reported.